Embodiments of the present invention relate to the field of medical imaging using radiation and more particularly, related to the estimation and monitoring of radiation doses to which a body or some organs thereof are subjected, when acquiring images by means of a radiation imaging system.
Exposure of a patient to X-rays produces two types of effects: stochastic, long-term effects (cancer risk) are related to the dose accumulated by patients throughout their lifetime, from this perspective, any radiation dose must be weighed against the benefit for the patient, and short-term effects over the hours, days and weeks following after exposure (burns), these are related to short-time exposure at very high dose.
Yet, radiation imaging can expose a patient's body or some parts thereof to radiation doses which may vary substantially from one acquisition to another, particularly in relation to the chosen directions of exposure.
Also, radiation and notably X-rays interact very differently with the bones or tissues of the human body, preventing easy understanding of the level of radiation to which a given part of the body can still be exposed.
There is therefore a need for the monitoring of radiation doses received by a body or by different parts thereof during an examination involving one or more acquisitions of radiological images.
It is also desired, when acquiring new images, to avoid accumulating too excessive radiation doses in some body regions or in some organs, and hence to be able to determine the acquisition conditions for subsequent images allowing optimization of the radiation doses accumulated in a body.
Fluoroscopy uses a continuous or series of pulsed X-ray beam used to image movement of organs and objects within the body. Fluoroscopically guided minimally invasive procedures have become common due to generally lower trauma and faster recovery compared to conventional surgery. Examples of Fluoroscopically Guided Interventional (FGI) procedures include percutaneous transluminal coronary angioplasty and radiofrequency (RF) ablation for treatment of cardiac dysrhythmias. Interventional procedures are often made in several exam sessions that are generally made within a period during which healing effects cannot be fully completed. In such case, the overall risk estimation can be a conservative cumulation of dose across these sessions. From one session to the next, patients are only approximately repositioned to the same location, so that the X-ray beam projections are not the same in all sessions and this leads to inaccuracy in dose estimation when these differences are not fully considered.
Methods are known to estimate the distribution of radiation doses accumulated in a patient's body. Radiation dose may be estimated by direct measurement using dosimeters located on the patient. Radiation reactive sheets of material provide resolution, but do not conform to the patient's body. Point dosimeters can be located on a patient, but are known to under sample radiation dose and have low sampling resolution. Mathematical models can be used to estimate radiation dose, but do have limited accuracy to account for patient size and location or radiation backscatter and therefore limited accuracy to cumulate patient dose across multiple exam sessions.